{"id":8323,"date":"2026-04-03T13:36:51","date_gmt":"2026-04-03T13:36:51","guid":{"rendered":"https:\/\/www.proefschriftmaken.nl\/portfolio\/kelly-stewart\/"},"modified":"2026-04-23T08:54:06","modified_gmt":"2026-04-23T08:54:06","slug":"kelly-stewart","status":"publish","type":"us_portfolio","link":"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/kelly-stewart\/","title":{"rendered":"Kelly Stewart"},"content":{"rendered":"","protected":false},"excerpt":{"rendered":"","protected":false},"author":8,"featured_media":13980,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"us_portfolio_category":[45],"class_list":["post-8323","us_portfolio","type-us_portfolio","status-publish","has-post-thumbnail","hentry","us_portfolio_category-new-template"],"acf":{"naam_van_het_proefschift":"Preventive genetic testing","samenvatting":"Er is geen Nederlandse samenvatting beschikbaar. De Engelse samenvatting vind je <a href=\"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/kelly-stewart\/\">hier<\/a>.","summary":"As the world is facing a challenging epidemic of non-communicable diseases, such as cancer, diabetes type 2, and cardiovascular diseases, primary prevention is becoming increasingly paramount. Important risk factors for these diseases include smoking, poor diet and physical inactivity. These risk factors are to a large extent modifiable and therefore pose targets for prevention.\n\nAt the same time, personalised health care is undergoing rapid developments. One interesting emerging field in that light is that of personalised genetic testing (PGT) for disease risks. These tests aim to estimate an individual\u2019s risk of developing a certain disease based on their genetic profile. These services are mostly offered online without interference of a health care professional (HCP), thereby referred to as direct-to-consumer genetic testing (DTC-GT). It has been hypothesised that if one learns to be at an increased risk of disease, they may be triggered to change their health behaviour. For example, a smoking individual may consider quitting when learning of an increased risk of lung cancer. In that way, PGT may be an important approach in the pursuit of preventing chronic diseases.\n\nIn this thesis I address different issues regarding PGT; from pre-test informed decision-making to the need for post-test counselling in achieving behaviour change. I conclude by proposing a new PGT service, Health Potential, as an alternative approach to address these issues.\n\nChapter 1 starts with a general introduction into the topic, introducing the issues surrounding PGT that are addressed in this thesis.\n\nChapter 2 starts at the pre-testing phase, where we studied characteristics of the expected consumer population of DTC-GT in order to provide assistance in the development of pre-test information to enhance informed decision-making. More particular, we studied factors associated with acceptability of, and consideration (some time in the future) and intention (<1 year) of undergoing DTC-GT. Multiple correlates were identified, but of particular interest is the finding that lower knowledge of genetic principles was associated with greater acceptability, and lower understanding of DTC-GT results was associated with greater consideration and intention. As for an informed decision, it is necessary that decisions are based on complete and relevant information, our results may indicate that informed decision-making may be hampered. The identified characteristics can be used in development and distribution of pre-test information, in order to help consumers make a truly informed decision.\n\nIn chapter 3, I move on to address the limitation of basing disease-risk predictions on genetic factors only, by reporting an overview of all genetic, lifestyle and environmental risk factors, using COPD as an example. This study gives an overview of the currently available evidence of lifestyle, environmental, and genetic factors associated with the development of COPD. We identified 274 genetic variants, of which 74% (n=204) showed a significant association with ORs ranging from 0.17-3.33. In addition, we identified nine different lifestyle and environmental factors, for which a significant association was found for eight, with ORs ranging from 0.45-9.50. In the light of personalised prevention, these results can be combined to make disease risk prediction more accurate.\n\nThen, chapter 4 reports the results of a systematic review with meta-analysis into different effects of DTC-GT, for which there has been a lot of discussion among academics and regulatory bodies: behaviour change, adverse psychological effects and post-test medical consumption. We found that overall 24% had a positive lifestyle change. More specifically, 16% and 12% had improved dietary and exercise practices respectively, whereas 19% quit smoking. In addition, 7% of participants had subsequent preventive checks. Finally 33% had shared their results with any health care professional and 50% had shared it with family and\/or friends. Although meta-analysis was not possible for psychological responses, results showed that anxiety, distress and worry were low or absent and that the effect faded with time. These results indicate that DTC-GT has potential to change behaviour, without great risk of adverse psychological responses, but that attention must be paid to avoid unnecessary downstream costs as a result of testing.\n\nIn chapter 5 I move on with improving actionability of results by including lifestyle advice based on modifiable risk factors for disease. I do so using bladder cancer as an example, in a systematic review with meta-meta-analysis of modifiable risk factors of bladder cancer. We found a great number of modifiable risk factors that were significantly associated with the development of bladder cancer: current (RR=3.14) or former (RR=1.83) cigarette smoking, pipe (RR=1.90) or cigar (RR=2.30) smoking, antioxidant supplementation (RR=1.52), obesity (RR=1.10), higher physical activity levels (RR=0.86), higher body levels of selenium (RR=0.61) and vitamin D (RR=0.75), and higher intakes of: processed meat (RR=1.22), vitamin A (RR=0.82), vitamin E (RR=0.82), folate (RR=0.84), fruit (RR=0.77), vegetables (RR=0.83), citrus fruit (RR=0.85), and cruciferous vegetables (RR=0.84). Finally, three occupations with the highest risk were tobacco workers (RR=1.72), dye workers (RR=1.58), and chimney sweeps (RR=1.53). In addition, we calculated a probability of causation, which can be interpreted as the percentage of exposed cases that are attributable to the exposure (e.g. the number of cases among smokers that are attributable to smoking). Probabilities of causation for individual factors ranged from 4%-68%. We also calculated a combined probability of causation, combining 4 non-overlapping factors: total fruit and vegetable consumption, processed meat consumption, smoking, and physical activity. This showed that up to 81.8% of the bladder cancer cases, among those with non-optimal lifestyle behaviours, could be prevented through lifestyle modifications. Together these results provide starting points for actionable behaviour change advice.\n\nFrom here I continue with the service we developed, Health Potential. This service is a PGT service that estimates personal disease risk of 20+ common chronic diseases, with both a genetic and lifestyle component of development. In contrast to DTC-GT, this service is obtained and delivered by a health care professional, who can (1) assist in pre-test decision-making to achieve an informed decision, (2) aid in interpreting of test results, and (3) offer (on-going) support to initiate and maintain behaviour change post-testing. Chapter 6 reports the study protocol for our Health Potential trial, in which we will test how effective our new Health Potential service is in changing behaviour and whether additional counselling is necessary to achieve and maintain behaviour change. The study consists of two integrated designs resulting in three study arms. Participants are clients of local prevention clinics, purchasing a personalised health check (PHC; intervention condition), consisting of Health Potential\u00ae and a general health check, or the general health check alone (GHC; control condition) (Part A). PHC participants will be randomised to receive four additional lifestyle counselling sessions over a period of three months (Part B). Results from this study can then provide valuable insights in possible ways forward in the field of personalised prevention.\n\nFinally, chapter 7 contains the general discussion, placing the findings in light of other research, as well as from an ethical perspective.\n\nTo conclude, PGT certainly has potential to fulfill multiple values; for consumers, HCPs and society alike. Nevertheless, we must maintain a critical view to ensure such services are implemented and utilised in a way that promotes benefits and fulfils individual values, while averting negative consequences. This thesis provided several directions as to how this can be approached.","auteur":"Kelly Stewart","auteur_slug":"kelly-stewart","publicatiedatum":"20 september 2018","taal":"EN","url_flipbook":"https:\/\/ebook.proefschriftmaken.nl\/ebook\/kellystewart?iframe=true","url_download_pdf":"","url_epub":"","ordernummer":"FTP-202604031333","isbn":"978-90-829118-0-0","doi_nummer":"","naam_universiteit":"Universiteit Maastricht","afbeeldingen":13980,"naam_student:":"","binnenwerk":"","universiteit":"Universiteit Maastricht","cover":"","afwerking":"","cover_afwerking":"","design":""},"_links":{"self":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/8323","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio"}],"about":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/types\/us_portfolio"}],"author":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/comments?post=8323"}],"version-history":[{"count":1,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/8323\/revisions"}],"predecessor-version":[{"id":8324,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/8323\/revisions\/8324"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media\/13980"}],"wp:attachment":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media?parent=8323"}],"wp:term":[{"taxonomy":"us_portfolio_category","embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio_category?post=8323"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}